The present invention relates to a fuel injection advance angle control apparatus for an internal combustion engine such as a Diesel engine.
Fuel injection systems are popular in the field of internal combustion engines due to their many advantages, especially where adapted to combustion ignition or Diesel engines. Typical of such systems is the distribution system in which a plunger is simultaneously rotated and reciprocated to pump fuel to injection nozzles of a number of engine cylinders.
The performance and efficiency of the engine depend on fuel injection at the right time and in the right amount. The problem is complicated by the fact that the proper time for fuel injection is a function not only of engine speed but also engine operating conditions such as starting, idling, high speed running and the like.
Generally, it is necessary to progressively increase the fuel injection advance angle as the engine speed increases. What is meant by the advance angle is the relative angular position in the engine operating cycle at which fuel injection is initiated and may be considered as the number of degrees before the engine piston reaches top dead center at which fuel injection begins. In addition to the basic relationship between advance angle and engine speed, it is also necessary to advance the angle upon starting the engine and retard the angle for idling.
A known system for achieving this operation comprises an engine driven pump which pumps fuel from a reservoir or tank at a pressure which increases with engine speed. The pressurized fuel is applied to a spring loaded piston which is connected to an advance angle control mechanism. The fuel pressure balanced against the spring force positions the piston which in turn sets the advance angle at a value which corresponds to the position of the piston. In this manner, the advance angle is increased as the engine speed increases.
The advance angle is increaed upon starting by another spring loaded piston which moves the main piston to an advanced position at low engine speed. As the engine speed and fuel pressure increase, the secondary piston is retracted and the main piston allowed to move to a retarded position for constant speed idling. Further increase in the engine speed and fuel pressure cause the main piston to be moved from the retarded position in the normal manner to increase the advance angle.
A problem in this basic system is that the fuel pressure increases quickly upon starting and the advance angle is changed from the advanced to the retarded value before stable combustion is attained in the engine. This results in extreme difficulty in starting the engine since the advance angle is retarded prematurely while the engine temperature is still low.